Exterior insulation and finish systems (EIFS) account for an estimated 30 percent of commercial exteriors nationwide and, despite setbacks due to early moisture problems, are still gaining popularity in the residential market. A durable, never-needs-painting exterior is very appealing to homeowners and the energy-saving benefit of foam insulation is also a big plus.
While some are content with the austere, modern look that comes standard with flat, monochromatic stucco covering the entire house, others, such as my recent clients' Realtor, think that trim is necessary around windows and doors to make a house sellable. The challenge I was faced with was applying trim to a textured surface around recessed windows whose stucco surfaces weren't always square and straight without damaging the waterproof exterior shell applied more than a decade before or requiring a color touch-up to the now-faded surface. Adding to the difficulty, my maintenance-wary client had chosen fiber-cement trimboards 5-1/2 inches wide and a full 1 inch thick. Not the lightest of materials to apply over the 2-inch-thick foam wall.
It took some thought to determine how to complete the job with permanent, low-maintenance trim that shed water effectively and didn't compromise the watertight stucco behind it. But the solution I developed was both elegantly simple and nearly foolproof to install: Pre-build and pre-paint the face trim like giant picture frames to make sure they were square, flush-edged, and easy to hang with a minimum of fastener intrusion into the foam and with the least possibility of crushing the foam and cracking the stucco surface.
Since the window reveal was a minimal 1 inch, I decided to hang surface-mounted face frames only and simply paint the reveal the same color. This also kept the exterior window opening as large as possible. Chamfering the top edges of the two horizontal pieces and butting the frame pieces together in the right way meant there would be no easy route for water to enter the assembled trim. And with the frames completed on the ground, the primer and two topcoats were easy and quick to apply with a roller with no masking, touch-up, or tedious work on a ladder.
By measuring the width of each finished opening in several places against the stucco, I determined an average measurement. For the height, I went with the longest measurement so the bottom horizontal wouldn't be able to trap water behind it anywhere along its width. After cutting and labeling all of the pieces, I ripped a 5-degree bevel along the top edges of the horizontal members with a table saw. Make sure to shave off all factory ends as they are not suitable for accurate joints.
To build the frames square and stiff with butt joints, I used pocket screws and polyurethane adhesive. A test joint with your adhesive of choice would be wise as fiber-cement manufacturers usually won't recommend any adhesive for their products. I found better results when sanding off the primer surface and cleaning off the dust before applying any glue. For the 1-inch-thick trim I used, I had to find oddball 2-inch screws, but since then, they have become available from pocket-screw makers.
When building the frames, it was important to line up the face sides of the trim, and since a fiber-cement board can vary noticeably in thickness, I clamped the pieces down to a thick piece of plywood to provide a flat reference surface. I also made sure the plywood was square to make it easier to lay out the corner assembly by aligning the pieces along the edges of the plywood. After lining up two corner pieces and checking them for square, I clamped everything down, including the pocket-hole jig. Typical pocket-hole bits will not make a pilot hole deep enough to keep the fiber-cement board from splitting when the screw is driven in, so make sure to drill a little deeper with a second bit marked for the correct depth. I used a long bell hanger's bit fed right through the center of the jig's guide hole so I could make sure my angle stayed consistent.
The other option is to use a standard bit once the boards and jig are unclamped, but make sure to keep the correct angle so that tightening the screw doesn't lever the faces out of the same parallel plane. And since this product and your time are expensive, remember to make a test joint to determine the correct setback of the drilling jig, the proper collar clamp position on the pocket-hole bit, and the depth marking for the pilot bit. For the strongest joint in this soft material, leave enough thickness under the head of the screw in the pocket hole so it doesn't tear out when the screw compresses it. If you strip out a hole while tightening a screw, blow the dust out, squirt some CA (instant-cure) glue into the hole, and try the screw again in a few minutes. To prevent such stripping, start the screws with your cordless drill/driver at its lowest torque setting and finish them all by hand. Just snug up the joint and then let the glue dry before really handling the frames.
After assembly, priming, and painting, I drilled countersink holes deeper than the head of the screws so they could be filled flat after installation. I allowed about 18 inches between screws typically, but it was important to have one located dead center on the top for the installation technique.
After cleaning the backs of the frames and of the walls where the trim would touch, I was ready to hang them. It helps to have two people for this, one at the top center and one at a bottom corner. Take the frame up your ladder along with a pencil, level, hammer, and some 16d common nails. Find the center placement by feel and eye, averaging out any slight ins and outs of the stucco surface. Find the height by aligning the top edge of the bottom piece with the lowest point of the stucco sill for good drainage. Holding the piece steady, check it with the level.
From my experience, it will already be very close. Tweak the placement if necessary and remember to keep everything relatively centered right to left and at the correct height relative to the sill. When the position is correct, pound a nail into the top center hole. This will hold the frame while you double check the level. If your frame is very wide or made of smaller fiber-cement board, it may bow if hung in the center only. In this case, additional nails should be driven into each vertical piece or the frame should be supported by your helper during the alignment and marking process. Use the level on top to check for bowing in any case. Mark a bottom corner with the pencil along both sides and pound a nail gently into each hole. These nails only have to penetrate the stucco and foam. With each hole made and a corner marked, pull out the center nail and bring the frame back down.
Apply a bead of the EIFS manufacturer's–recommended caulk close to the inside and outside perimeters on the back of the frame and zigzag construction adhesive in between. With the smallest possible opening on another tube, inject the same caulk into the nail holes in the foam until totally full. Start your screws in the holes of the trim before you ascend the ladder again with the center top one protruding a couple of inches to help you line up the frame. I used 4-inch-long screws for the 2-inch foam, but thicker foam or trim will dictate the use of a longer screw. While snugging up the center screw, use the pencil marks at the corner to align the frame so the caulk and glue do not smear on the finished wall or break their perimeter seal.
The remaining screws should all find their holes easily and will extrude a little caulk near the head when driven tight, totally sealing the hole they are in. The tremendous amount of surface area of the caulk and adhesive should provide plenty of actual holding power so the screws are essentially acting as clamps until everything sets and need not be driven in very tight. This low pressure per surface area of a pre-built frame keeps the waterproof stucco shell intact and results in a flatter, squarer trim-out than you could get piecing it together on the wall.
A bead of approved trim-colored or paintable caulk around both the inside edges and the periphery and a quick fill over each screw head should be all that's needed to complete this long-lasting, low-maintenance trim.